pith. sign in

arxiv: 1907.06397 · v1 · pith:4AH3GUFBnew · submitted 2019-07-15 · 🪐 quant-ph

Self-testing of symmetric three-qubit states

Pith reviewed 2026-05-24 21:43 UTC · model grok-4.3

classification 🪐 quant-ph
keywords self-testingsymmetric three-qubit statesW stateGHZ statedevice-independent certificationswap methodsemidefinite programming
0
0 comments X

The pith

Symmetric three-qubit states that superpose the W and GHZ states can be self-tested device-independently from their measurement statistics.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes self-testing protocols for the family of symmetric three-qubit states formed as superpositions of the W state and the GHZ state. For the special case of equal coefficients in the computational basis, an analytic criterion proves uniqueness by combining subsystem self-testing on a partially entangled state and a maximally entangled state at the same time. For arbitrary coefficients the same uniqueness is shown numerically to high precision by applying the swap method inside a semidefinite program. The only data used are the number of measurements, the number of outcomes per measurement, and the observed probabilities.

Core claim

We propose self-testing schemes for a large family of symmetric three-qubit states, namely the superposition of W state and GHZ state. We first propose and analytically prove a self-testing criterion for the special symmetric state with equal coefficients of the canonical basis, by designing subsystem self-testing of partially and maximally entangled state simultaneously. Then we demonstrate for the general case, the states can be self-tested numerically by the swap method combining semi-definite programming (SDP) in high precision.

What carries the argument

Analytic self-testing criterion obtained by simultaneous subsystem self-testing of a partially entangled two-qubit state and a maximally entangled two-qubit state (equal-coefficient case); swap method inside semidefinite programming (general case).

If this is right

  • The equal-coefficient symmetric state admits a fully analytic self-testing proof.
  • Arbitrary superpositions of W and GHZ admit high-precision numerical self-testing.
  • Self-testing now covers a continuous family of symmetric three-qubit states rather than isolated examples such as pure Dicke or graph states.
  • Certification requires only the number of measurements, the number of outputs, and the observed statistics.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Device-independent protocols that consume these states as resources could be certified without trusting the state-preparation devices.
  • The same combination of analytic subsystem arguments and numerical SDP may extend self-testing to other continuous families of symmetric multipartite states.
  • Exact analytic criteria found for special coefficient values can serve as benchmarks for checking the accuracy of numerical SDP relaxations on nearby states.

Load-bearing premise

The observed statistics are assumed to arise exactly from the claimed projective measurements performed on the target symmetric state.

What would settle it

Exhibiting a different three-qubit state (or a higher-dimensional state) together with measurements that produce exactly the same joint probability tables would falsify the uniqueness claim.

Figures

Figures reproduced from arXiv: 1907.06397 by Fei Gao, Qiaoyan Wen, Xinhui Li, Yukun Wang, Yunguang Han.

Figure 1
Figure 1. Figure 1: FIG. 1. The swap circuit. The local isometry used to self-tes [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. (Color Online) The plot of lower bounds on the fi [PITH_FULL_IMAGE:figures/full_fig_p007_3.png] view at source ↗
read the original abstract

Self-testing refers to a device-independent way to uniquely identify the state and the measurement for uncharacterized quantum devices. The only information required comprises the number of measurements, the number of outputs of each measurement, and the statistics of each measurement. Earlier results on self-testing of multipartite state were restricted either to Dicke states or graph states. In this paper, we propose self-testing schemes for a large family of symmetric three-qubit states, namely the superposition of W state and GHZ state. We first propose and analytically prove a self-testing criterion for the special symmetric state with equal coefficients of the canonical basis, by designing subsystem self-testing of partially and maximally entangled state simultaneously. Then we demonstrate for the general case, the states can be self-tested numerically by the swap method combining semi-definite programming (SDP) in high precision.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 0 minor

Summary. The paper proposes self-testing schemes for a large family of symmetric three-qubit states, namely superpositions of the W state and GHZ state. It analytically proves a self-testing criterion for the special case with equal coefficients by simultaneous subsystem self-testing of partially and maximally entangled states. For general coefficients, it demonstrates self-testing numerically via the swap method combined with semi-definite programming (SDP) in high precision.

Significance. The analytic proof for the equal-coefficient special case is a strength, as it supplies a rigorous uniqueness result grounded in standard quantum mechanics and self-testing definitions without free parameters or fitted quantities. This extends self-testing beyond the previously considered Dicke and graph states. The numerical SDP results for the general family provide supporting evidence of practical utility but do not rise to the level of a uniqueness proof.

major comments (1)
  1. [Abstract] Abstract: The numerical demonstration for general coefficients via the swap method and SDP in high precision does not establish rigorous uniqueness. SDP relaxations are outer approximations to the set of quantum correlations, and floating-point results are never exactly tight; therefore high-precision numerics alone cannot exclude the existence of other states or measurements that reproduce the observed statistics within the reported tolerance. This concern is load-bearing for the central claim that covers the large family of states.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the careful reading and constructive feedback. We appreciate the positive assessment of the analytic proof for the equal-coefficient case. We agree that the numerical SDP results constitute supporting evidence rather than a rigorous uniqueness proof, and will revise the manuscript to clarify this distinction in the abstract and discussion.

read point-by-point responses
  1. Referee: [Abstract] Abstract: The numerical demonstration for general coefficients via the swap method and SDP in high precision does not establish rigorous uniqueness. SDP relaxations are outer approximations to the set of quantum correlations, and floating-point results are never exactly tight; therefore high-precision numerics alone cannot exclude the existence of other states or measurements that reproduce the observed statistics within the reported tolerance. This concern is load-bearing for the central claim that covers the large family of states.

    Authors: We agree with the referee. The SDP-based numerical demonstration supplies high-precision evidence but cannot rigorously establish uniqueness, as correctly noted regarding relaxations and floating-point precision. In the revised manuscript we will update the abstract to state that the general family is supported by numerical evidence via the swap method and SDP (rather than claiming it establishes self-testing with the same rigor as the analytic case), and we will add a brief discussion of this limitation in the conclusions. revision: yes

Circularity Check

0 steps flagged

No circularity: analytical construction and numerical SDP are independent of target state by definition.

full rationale

The manuscript derives its self-testing criterion for the equal-coefficient case via an explicit analytical construction of simultaneous subsystem self-testing on partially and maximally entangled states; this is a direct proof from observed correlations and does not reduce to the target state by construction or by fitting. The general-coefficient case is handled by the standard swap-method SDP relaxation, which is an external numerical verification tool rather than a self-referential fit or self-citation. No load-bearing self-citation, ansatz smuggling, or renaming of known results appears; the derivation chain remains self-contained against standard quantum-information benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The work rests on the standard axioms of quantum mechanics and the operational definition of self-testing; no additional free parameters or invented entities are introduced in the abstract.

axioms (1)
  • standard math Quantum mechanics with projective measurements and the operational definition of self-testing from statistics alone.
    Invoked throughout the abstract as the foundation for the proposed criteria.

pith-pipeline@v0.9.0 · 5672 in / 1029 out tokens · 17095 ms · 2026-05-24T21:43:35.850649+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

34 extracted references · 34 canonical work pages · 2 internal anchors

  1. [1]

    0" or "1

    with different kinds of coefficients. A. Self-testing of a symmetric three-qubit state The specific case we consider is the state with equal coefficient of the basis, reads as: |ψ ⟩ = 1√ 5 (|001⟩ + |010⟩ + |100⟩ + |000⟩ + |111⟩). (9) The basic idea of self testing this state is to project the state onto two kinds of subsystem entangled states by one FIG. 1. The...

  2. [2]

    (35) Observation (16a) implies ⟨P 1 CA2(B2 − B1)⟩ = 0 ⇒ P 1 CX ′ A |ψ ⟩ ⊥ P 0 CZ ′ B |ψ ⟩ (36) and combine the first relation in ( 34), we have P 1 CX ′ A |ψ ⟩ ⊥ P 1 CZ ′ A |ψ ⟩

    implies P 1 CZ ′ A |ψ ⟩ =P 1 CZ ′ B |ψ ⟩, P 1 CX ′ A |ψ ⟩ =P 1 CX ′ B |ψ ⟩ (34) and the anti-commutation relations P 1 CZ ′ AX ′ A |ψ ⟩ = −P 1 CX ′ AZ ′ A |ψ ⟩, P 1 CZ ′ BX ′ B |ψ ⟩ = −P 1 CX ′ BZ ′ A |ψ ⟩. (35) Observation (16a) implies ⟨P 1 CA2(B2 − B1)⟩ = 0 ⇒ P 1 CX ′ A |ψ ⟩ ⊥ P 0 CZ ′ B |ψ ⟩ (36) and combine the first relation in ( 34), we have P 1 CX ...

  3. [3]

    This state can be normalized into the form of |junk⟩ABC ⊗ |ψ ⟩A′B′C ′, here |junk⟩ = √ 5P 0 AP 0 BP 0 C |ψ ⟩

    to |Ψ′⟩ =P 0 AP 0 BP 0 C |ψ ⟩ (|000⟩ + |001⟩ + |010⟩ + |100⟩ + |111⟩). This state can be normalized into the form of |junk⟩ABC ⊗ |ψ ⟩A′B′C ′, here |junk⟩ = √ 5P 0 AP 0 BP 0 C |ψ ⟩. Thus, we have proven that, with these requirements (15)–( 21) on the measurement results indeed self-test the unknown state as target state ( 9). Further more, we also consider...

  4. [4]

    localizing ma- trix

    and ( 48), where Γ is a matrix with NPA hierarchy characterization of the quantum behaviors. This moment matrix corre- sponding to q-local level 1 (which includes any products with at most one operator per party) has size 74 × 74 7 and is augmented by necessary terms(like ⟨ZAXAZA⟩, ⟨ZBXBZCXC⟩, ⟨ZCXCZAXAZA⟩ and so on) to express all the average values ⟨·⟩t...

  5. [5]

    (57) Define |j′ A⟩ ≡ ∑ j Uji |j⟩, |k′ B⟩ ≡ ∑ k Vik |k⟩ and λ i = Sii, for i,j,k ∈ { 0, 1}

    0 0 √ 1 6 (3 − √ 5)   (56) is diagonal, U and V are unitary matrices: U =   3+ √ 5 2 √ 5+2 √ 5 3− √ 5 2 √ 5− 2 √ 5 1+ √ 5 2 √ 5+2 √ 5 1− √ 5 2 √ 5− 2 √ 5  , V =   1+ √ 5 2 √ 5+ √ 5 1− √ 5√ 10− 2 √ 5√ 2 5+ √ 5 5+ √ 5 10  . (57) Define |j′ A⟩ ≡ ∑ j Uji |j⟩, |k′ B⟩ ≡ ∑ k Vik |k⟩ and λ i = Sii, for i,j,k ∈ { 0, 1}. Obviously, {|j′⟩}A and {|k′⟩}B are ...

  6. [6]

    Quantum entanglement

    Horodecki R, Horodecki P, Horodecki M, et al. Quantum entanglement. Reviews of modern physics, 2009, 81(2): 865

  7. [7]

    Teleport- ing an unknown quantum state via dual classical and Einstein-Podolsky-Rosen channels

    Bennett C H, Brassard G, Crépeau C, et al. Teleport- ing an unknown quantum state via dual classical and Einstein-Podolsky-Rosen channels. Physical review let- ters, 1993, 70(13): 1895

  8. [8]

    Classical command of quantum systems

    Reichardt B W, Unger F, Vazirani U. Classical command of quantum systems. Nature, 2013, 496(7446): 456

  9. [9]

    Public quantum com- munication and superactivation

    Brandao F G S L, Oppenheim J. Public quantum com- munication and superactivation. IEEE Transactions on Information Theory, 2012, 59(4): 2517-2526

  10. [10]

    Scalable quantum search using trapped ions

    Ivanov S S, Ivanov P A, Linington I E, et al. Scalable quantum search using trapped ions. Physical Review A, 9 2010, 81(4): 042328

  11. [11]

    Spin state tomog- raphy of optically injected electrons in a semiconductor

    Kosaka H, Inagaki T, Rikitake Y, et al. Spin state tomog- raphy of optically injected electrons in a semiconductor. Nature, 2009, 457(7230): 702

  12. [12]

    The device-independent outlook on quantum physics

    Scarani V. The device-independent outlook on quantum physics. Acta Physica Slovaca, 2012, 62(4): 347-409

  13. [13]

    Proposed ex- periment to test local hidden-variable theories

    Clauser J F, Horne M A, Shimony A, et al. Proposed ex- periment to test local hidden-variable theories. Physical review letters, 1969, 23(15): 880

  14. [14]

    Some results and problems on quan- tum Bell-type inequalities

    Tsirelson B S. Some results and problems on quan- tum Bell-type inequalities. Hadronic Journal Supple- ment, 1993, 8(4): 329-345

  15. [15]

    Self testing quantum apparatus

    Mayers D, Yao A. Self testing quantum apparatus. arXiv preprint quant-ph/0307205, 2003

  16. [16]

    Robust self-testing of unknown quantum systems into any entangled two-qubit states

    Yang T H, Navascués M. Robust self-testing of unknown quantum systems into any entangled two-qubit states. Physical Review A, 2013, 87(5): 050102

  17. [17]

    Sum-of-squares decompositions for a family of Clauser-Horne-Shimony-Holt-like inequalitie s and their application to self-testing

    Bamps C, Pironio S. Sum-of-squares decompositions for a family of Clauser-Horne-Shimony-Holt-like inequalitie s and their application to self-testing. Physical Review A, 2015, 91(5): 052111

  18. [18]

    All pure bipartite entangled states can be self-tested

    Coladangelo A, Goh K T, Scarani V. All pure bipartite entangled states can be self-tested. Nature communica- tions, 2017, 8: 15485

  19. [19]

    Optimal robust quantum self-testing by binary nonlocal XOR games

    Miller C A, Shi Y. Optimal robust quantum self- testing by binary nonlocal XOR games. arXiv preprint arXiv:1207.1819, 2012

  20. [20]

    All the self-testings of the singlet for two binary measurements

    Wang Y, Wu X, Scarani V. All the self-testings of the singlet for two binary measurements. New Journal of Physics, 2016, 18(2): 025021

  21. [21]

    Robust self-testing of the singlet

    McKague M, Yang T H, Scarani V. Robust self-testing of the singlet. Journal of Physics A: Mathematical and Theoretical, 2012, 45(45): 455304

  22. [22]

    Analytic and nearly optimal self-testing bounds for the Clauser-Horne-Shimony-Holt and Mer- min inequalities

    Kaniewski J. Analytic and nearly optimal self-testing bounds for the Clauser-Horne-Shimony-Holt and Mer- min inequalities. Physical review letters, 2016, 117(7): 070402

  23. [23]

    Physical char- acterization of quantum devices from nonlocal correla- tions

    Bancal J D, Navascué M, Scarani V, et al. Physical char- acterization of quantum devices from nonlocal correla- tions. Physical Review A, 2015, 91(2): 022115

  24. [24]

    Robust and versa- tile black-box certification of quantum devices

    Yang T H, Vértesi T, Bancal J D, et al. Robust and versa- tile black-box certification of quantum devices. Physical review letters, 2014, 113(4): 040401

  25. [25]

    Self-testing graph states

    McKague M. Self-testing graph states. Conference on Quantum Computation, Communication, and Cryptog- raphy. Springer, Berlin, Heidelberg, 2011: 104-120

  26. [26]

    Self-testing multipartite entangled states through projections onto two systems

    Šupić I, Coladangelo A, Augusiak R, et al. Self-testing multipartite entangled states through projections onto two systems. New Journal of Physics, 2018, 20(8): 083041

  27. [27]

    Generalized Schmidt decomposition and classification of three- quantum-bit states

    Acín A, Andrianov A, Costa L, et al. Generalized Schmidt decomposition and classification of three- quantum-bit states. Physical Review Letters, 2000, 85(7): 1560

  28. [28]

    Three-qubit pure- state canonical forms

    Acín A, Andrianov A, Jané E, et al. Three-qubit pure- state canonical forms. Journal of Physics A: Mathemati- cal and General, 2001, 34(35): 6725

  29. [29]

    Almost every pure state of three qubits is completely determined by its two- particle reduced density matrices

    Linden N, Popescu S, Wootters W K. Almost every pure state of three qubits is completely determined by its two- particle reduced density matrices. Physical review letter s, 2002, 89(20): 207901

  30. [30]

    Three qubits can be entangled in two inequivalent ways

    Dür W, Vidal G, Cirac J I. Three qubits can be entangled in two inequivalent ways. Physical Review A, 2000, 62(6): 062314

  31. [31]

    Testing the structure of multipartite entanglement with Bell inequalities

    Brunner N, Sharam J, Vertesi T. Testing the structure of multipartite entanglement with Bell inequalities. Physi- cal review letters, 2012, 108(11): 110501

  32. [32]

    Robust self-testing of the three-qubit W state

    Wu X, Cai Y, Yang T H, et al. Robust self-testing of the three-qubit W state. Physical Review A, 2014, 90(4): 042339

  33. [33]

    Self-testing of quantum systems: a review

    Šupić I, Bowles J. Self-testing of quantum systems: a review. arXiv preprint arXiv:1904.10042, 2019

  34. [34]

    A convergent hierarchy of semidefinite programs characterizing the set of quan- tum correlations

    Navascués M, Pironio S, Acín A. A convergent hierarchy of semidefinite programs characterizing the set of quan- tum correlations. New Journal of Physics, 2008, 10(7): 073013